The present invention provides a method of polishing a film by supplying a liquid on a surface of the film to be polished, and to method of adding a polishing liquid on a surface of the film.
The formation of the three-dimensional multilevel interconnections requires a planerization of the surface of the inter-layer insulator such as silicon oxide film. An aluminium wiring layer as a first bottom layer is formed thereafter a silicon oxide film is deposited by a chemical vapor deposition on the first layer. As a result, the silicon oxide film has an irregularity due to the aluminium wiring layer. When forming a second aluminium wiring layer on the irregular surface of the silicon oxide film through photo-lithography and dry etching processes, problems arise as to difficulty in focusing for exposure to be used for photo-resist pattern and as to difficulty in removal by dry etching of unnecessary part of the aluminium layer to form the second aluminium wiring layer. To solve these problems, it was proposed to conduct a polishing of a surface of the silicon oxide film before the aluminium wiring layer is formed thereon. This is disclosed in the Japanese Patent Application No. 4-94677. The polishing of the silicon oxide film is carried out by a chemical etching function and a mechanical friction function of polishing particles. As disclosed in the Japanese laid-open patent publication No. 4-5338, a polishing liquid is used wherein silica particles having a diameter of 20 nanometers are dispersed into an ammonium solution at 10 to 30 wt %.
Shortening the polishing time requires a high polishing speed which further requires large size silica particles. The use of the large size silica particles may result in damage to the surface of the film polished. Further, as illustrated in FIG. 1, the large silica particles give rise to the problem of a high speed precipitation thereof whereby a continuous stirring of the liquid is required. The continuous stirring of the liquid requires the polishing apparatus to be provided with a stirring system thereby resulting in a complicated structure of the polishing apparatus.
On the other hand, as disclosed in the Japanese laid-open patent publication No. 51-28295, when fine silica particles are used for polishing, there is no damage to the polishing surface, but there is a problem as to a low speed of the polishing.
A method of increasing a polishing speed without use of a large size polishing particle was proposed wherein an aggregation agent of an electrolytic salt is added into a slurry to cause an aggregation of silica particles to form large size aggregated particles to be used for polishing as illustrated in FIG. 2. This method is, however, has the disadvantage the necessity conduct a continuous stirring of the polishing liquid.